Navigation graph hos in multi activity

For Navigation components with multiple-activities, you shouldn't start activities using Intents, instead, you need to add activities as destinations to the nav_graph.

Should I create for each activity a navigation host graph or there are a way to use only one nav graph for 2 activities ?

Yes you should, for n activities, you should have n nav graphs, or less (in case you need to make some activities like normal activities that are not involved in the navigation)

So, in your case you have 2 activities, then you should have nav_grap1 & nav_grap2.

And supposing you need to move from activity1, fragment1 to activity2, then what you need to do:

• In nav_graph1 add <activity2> as a destination.
• Create an action in nav_graph1 from fragment1 to activity2

The nav graph of activity1 should look to something like:

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/navigation"
    app:startDestination="@id/fragment1_1">

    <fragment
        android:id="@+id/fragment1_1"
        android:name="com.example.android.xx.Fragment1_1"
        android:label="Fragment1_1" >

        <action
            android:id="@+id/action_fragment1_1_to_secondActivity"
            app:destination="@id/secondActivity" />

    </fragment>

    <fragment
        android:id="@+id/fragment1_2"
        android:name="com.example.android.xx.Fragment1_2"
        android:label="Fragment1_2" />

    <activity
        android:id="@+id/secondActivity"
        android:name="com.example.android.xx.SecondActivity"
        android:label="SecondActivity" />

</navigation>

• Whenever you want to move to activity2, then just use the different navigate() methods of the navigationController; for instance:

findNavController().navigate(R.id.action_fragment1_1_to_secondActivity)

For more info check documentation, and check this question

You can use an Intent to move from Activity 1 to Activity 2.

Each Activity will need its own NavGraph to host and navigate within the 3 Fragments. So will you will be using Navigation Component to move from one fragment to another within the hosting Activity.

You may also to decide to just have One Activity if your Architecture allows.